Persons requiring treatment of certain kinds of respiratory conditions frequently need to have medications delivered directly to the lungs. Nebulized or aerosolized solutions are the preferred method of delivery of respiratory medication because the medicant is fragmented into small particles that are more efficiently deposited near sites of drug activity in the lungs.
While nebulizers are well known to those skilled in the art, aerosolization of medications in a nebulizer is effected by putting a liquefied medication into a container or liquid reservoir and introducing a pressurized flow of gas through an aerosol nozzle carried within a nebulization chamber which is coupled to the liquefied medication contained in the liquid reservoir by a liquid draw tube. As the pressurized high velocity gas flows through the aerosol nozzle, the liquefied medication is drawn through the liquid draw or aspirator tube into the path of the high velocity gas and is fractured thereby into a mist, becoming entrained with the gas flow out of the nebulization chamber through the container and out therefrom through an output port.
In certain applications, nebulization therapy can be enhanced through the use of an auxiliary gas to supplement the nebulizing or driving gas being introduced through the aerosol nozzle. Such supplemental gases may be air, oxygen, helium or a combination of these two gases, referred to as heliox, depending upon the particular driving gas being used. The use of helium, an inert and metabolically stable gas which readily diffuses into swollen airways, or heliox, as a supplement to the nebulizing gas is also known, and these gasses are frequently used to drive the nebulized medication deeper into a user's lungs to deliver medications to bypass obstructed or restricted airways for a greater and more rapid effect from the medication.
One of the problems encountered when using supplemental gases, however, is that the injection of the supplemental gas into the nebulizing gas or into the nebulizing chamber affects the rate at which the liquefied medication passes out from the container through the aerosol output port. Generally, the rate at which the liquefied medication is to be nebulized and delivered to the user, is determined based upon, among other factors, the rate of flow and density of the driving or nebulizing gas being introduced into the nebulization chamber. When a supplemental gas is introduced into the nebulizing gas flow or into the nebulization chamber, the total quantity of medication delivered through the nebulization chamber changes. Accordingly, the predetermined rate at which the liquefied medication is discharged through the aerosol output port varies from that at which it was initially set.
Another problem encountered when a supplemental gas is introduced into a nebulizer breathing system, is that the supplemental gas is introduced at a point in the system close to the patient interface, such as a non-rebreathing (NRB) mask. The introduction of a supplemental gas at such a position relative to the NRB mask frequently results in the application of a non-uniform gas mixture. If a patient does not take uniform breaths, or the patient's breathing pauses, the percentage of the supplemental gas being introduced increases, or spikes, resulting in the patient inhaling a greater percentage of the supplemental gas with the next breath.